1. Field of the Invention
This invention relates to a circuit arrangement for the control of crypto operation in the case of procedure-controlled semi-duplex data transmission systems, and is more particularly concerned in such systems in which data are transmitted from the first station with a first data device and a first crypto device, via a transmission path, to a second station having a second crypto device and a second data device. Changes in the data transmission direction are signaled with an order which is transmitted from the first crypto device to the second crypto device and which is evaluated with an order evaluator. A control signal is emitted by way of an output of the second data device, whereby the control signal prepares the second crypto device for transmission when an end character is transmitted from the first data device to the second data device.
2. Description of the Prior Art
In the case when data is to be transmitted from the first station to a second station within the framework of a procedure control and in the case of semi-duplex operation, a starting character is first transmitted and the data then follows. Then, an end character from which the second station can recognize the end of the data transmission in this transmission dlirection is emitted. In order to signal a transmission direction change effected hereafter, an order word is transmitted from the first crypto device to the second crypto device, and thus the crypto generators of both stations are stopped in a character correct manner. During the transmission of desired bit flows, it cannot generally be prevented that bit patterns occur which are accidentally equal to the order word. In the case of prior art procedure controlled data transmission systems of this kind, accidentally occurring order words cause an undesired stopping of the receiving side crypto generator, before the occurrence of the end character. Due to this undesired stopping of the receiving side crypto generator, the effectiveness of the data transmission system is lowered.